1. Field of the Invention
The present invention relates to the liquid crystal display technology, and in particular to a method and a backlight module that achieve high color saturation of an LCD (Liquid Crystal Display) device.
2. The Related Arts
Due to the fast development of the OLED (Organic Light-Emitting Diode) technology, LCD faces a variety of challenges. Compared to OLED, LCD is relatively weak in respect of thinning, curvedness, and color saturation. To improve the performance of LCD for matching OLED, focus has been increasingly placed in these respects.
Color saturation of liquid crystal is also referred to as color gamut, which indicates the vividness of color displayed by a liquid crystal display and is an important parameter of liquid crystal products. Color saturation is represented by a percentage obtained with the triangular area delimited by the three primary colors of a display on the CIE (Commission international de l'eclairage) chormaticity diagram being the numerator and the triangular area delimited by the three primary colors defined by NTSC (the Notional Television System Committee) being the denominator. Regarding to the color saturation of liquid crystal, the known techniques make use of adjustment of a color filter (CF) mounted atop a TFT (thin-film transistor) liquid crystal cell or adoption of high saturation LED light source (such as an LED containing red and green fluorescent powder, an LED containing multiple color chips or using a quantum dot to serve as fluorescent powder) to achieve high color saturation (90% as defined by NTSC) of an LCD.
Theoretically, to achieve high color saturation is to expand the triangular area formed by color points of the pure colors (R, G, B) of an LCD as much as possible on the CIE chormaticity diagram in order to obtain an increased NTSC area. As shown in FIG. 1, a schematic view is given to demonstrate the behavior of RGB color points on the CIE chormaticity diagram for achieving high color saturation.
To expand the area formed by the color points of R, G, B of a module, two ways may be adopted. (1) For the spectra to which the color points of R, G, B of a module correspond, the half peak width can be reduced (so that the color coordinate can be made closer to the edges of the CIE chormaticity diagram); (2) The R wavelength that corresponds to the peak is made longer, the G wavelength closer to 520 nm, and the B wavelength shorter so that the area so formed is increased, namely NTSC gets higher and color saturation gets higher. Based on these two ways, the first way can be realized by increasing the thickness of the CF so as to reduce the half peak widths of R, G, B spectra, and further, the first and second ways can be simultaneously realized through adjustment of LED in order to improve color saturation.
In the known techniques, for the way of changing LED, an RG fluorescent powder included LED (an RG LED that contains two independent fluorescent emission peaks of R and G, a non-traditional YAG fluorescent emission being single peak) or a BR chip included LED (in addition to the blue chip traditionally contained in LED, a red chip being also contained), both can be integrated with the backlighting to combine with a conventional TFT cell (where for CF being not adjusted to work with the conventional backlighting, NTSC=72%), NTSC can reach 80-93%; however, it is not possible to achieve ultra-wide color gamut of 100%. Thus, further improvement is needed.
On the other hand, in the known techniques, a notch filter is capable of cut off a predetermined width for a given peak within the full band (namely the transmission of light is very close to zero in such a wave band), while the transmission rate in other bands remains high (namely the transmission rate >90%). Referring to FIG. 2, a transmission spectrum of a conventional notch filter is shown. It is observed that the cutoff center of the notch filter is 632.8 mm and the cutoff width is 30 nm.